Apply review feedback: clamp ambient-shadow opacity, fix neumorphic offsets, use IsNullOrWhiteSpace for shadow style

Agent-Logs-Url: https://github.com/jongalloway/DiagramForge/sessions/e947f672-253e-4984-bccb-969bbe3c7eca

Co-authored-by: jongalloway <68539+jongalloway@users.noreply.github.com>

Author: Copilot

src/DiagramForge/DiagramRenderer.cs

@@ -548,6 +548,8 @@ private static void ApplyShadowStyle(Theme theme, string shadowStyle)
                 theme.UseNodeShadows = true;
                 theme.ShadowOpacity = Math.Clamp(theme.ShadowOpacity <= 0 ? 0.50 : theme.ShadowOpacity, 0.30, 0.70);
                 theme.ShadowBlur = Math.Clamp(theme.ShadowBlur <= 0 ? 4.00 : theme.ShadowBlur, 2.00, 6.00);
+                theme.ShadowOffsetX = 0;
+                theme.ShadowOffsetY = 0;
                 break;
             case "frosted-glass":
                 theme.ShadowStyle = "frosted-glass";

src/DiagramForge/Rendering/SvgNodeWriter.cs

@@ -65,8 +65,8 @@ internal static void AppendNode(StringBuilder sb, Node node, Theme theme, int no
             && textOnlyObj is bool isTextOnly
             && isTextOnly;
         bool applyNodeShadow = theme.UseNodeShadows
-            && !string.IsNullOrEmpty(theme.ShadowStyle)
-            && !string.Equals(theme.ShadowStyle, "none", StringComparison.OrdinalIgnoreCase)
+            && !string.IsNullOrWhiteSpace(theme.ShadowStyle)
+            && !string.Equals(theme.ShadowStyle.Trim(), "none", StringComparison.OrdinalIgnoreCase)
             && !textOnly;
 
         sb.AppendLine($"""  <g transform="translate({SvgRenderSupport.F(node.X)},{SvgRenderSupport.F(node.Y)})">""");

src/DiagramForge/Rendering/SvgRenderSupport.cs

@@ -343,7 +343,7 @@ internal static void AppendShadowFilterDefs(
                 sb.AppendLine($"{indent}  <filter id=\"{shadowFilterId}\" x=\"-16%\" y=\"-12%\" width=\"140%\" height=\"148%\" color-interpolation-filters=\"sRGB\">");
                 sb.AppendLine($"{indent}    <feGaussianBlur in=\"SourceAlpha\" stdDeviation=\"{F(theme.ShadowBlur * 2.5)}\" result=\"blur\"/>");
                 sb.AppendLine($"{indent}    <feOffset in=\"blur\" dx=\"0\" dy=\"{F(Math.Max(theme.ShadowOffsetY, 3))}\" result=\"offset\"/>");
-                sb.AppendLine($"{indent}    <feFlood flood-color=\"{Escape(theme.ShadowColor)}\" flood-opacity=\"{F(theme.ShadowOpacity * 0.7)}\" result=\"shadow-color\"/>");
+                sb.AppendLine($"{indent}    <feFlood flood-color=\"{Escape(theme.ShadowColor)}\" flood-opacity=\"{F(Math.Clamp(theme.ShadowOpacity * 0.7, 0.0, 1.0))}\" result=\"shadow-color\"/>");
                 sb.AppendLine($"{indent}    <feComposite in=\"shadow-color\" in2=\"offset\" operator=\"in\" result=\"shadow\"/>");
                 sb.AppendLine($"{indent}    <feMerge>");
                 sb.AppendLine($"{indent}      <feMergeNode in=\"shadow\"/>");